Ceramic having a residual compressive stress for use in electronic devices

Abstract

A toughened ceramic component having a residual compressive stress and methods of forming the toughened ceramic component is disclosed. The ceramic component may include an internal portion having a first coefficient of thermal expansion (CTE) and an external portion substantially surrounding the internal portion and forming an exterior surface of the ceramic component. The external portion may have a second CTE that is less than the first CTE. Additionally, the external portion may be in compressive stress.

What is claimed is: 
     
       1. An electronic device, comprising:
 a housing having an opening; and 
 a transparent ceramic cover positioned at least partially within the opening and defining an exterior surface of the electronic device, the cover comprising:
 a singular sintered ceramic structure comprising:
 an external portion comprising a perimeter region and a center region, the perimeter region having a first thickness and the center region having a second thickness that is less than the first thickness; 
 an internal portion surrounded by the external portion; and 
 at least one of yttrium, silicon, germanium, or chromium dopant atoms distributed within the singular sintered ceramic structure, the dopant atoms having a first dopant concentration at the external portion and a second, lower dopant concentration at the internal portion, a concentration of dopant atoms decreasing from the first dopant concentration to the second dopant concentration to define a dopant gradient, wherein the external portion has a coefficient of thermal expansion that is different than a coefficient of thermal expansion of the internal portion. 
 
 
 
     
     
       2. The electronic device of  claim 1 , wherein the external portion has a lower coefficient of thermal expansion than the internal portion. 
     
     
       3. The electronic device of  claim 1 , wherein the external portion defines substantially all of a top surface and a bottom surface of the ceramic cover. 
     
     
       4. The electronic device of  claim 1 , wherein:
 a compressive residual stress of the transparent ceramic cover at the first portion is greater than a compressive residual stress of the transparent ceramic cover at the second portion. 
 
     
     
       5. The electronic device of  claim 1 , wherein the singular sintered ceramic structure comprises at least one of: zirconia, alumina (Al 2 O 3 ), silicon carbide, or silicon nitride. 
     
     
       6. The electronic device of  claim 1 , wherein the transparent ceramic cover is positioned over a display of the electronic device.